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Bioelectrical impedance analysis (BIA) is an established method for assessing integrity of biotissue. Adapting BIA as a diagnostic tool to monitor electrophysiological activity gives rise to evidence-based objective diagnostic approaches as opposed to visual assessment currently performed by practitioners in wound healing management. Advancements in the telecommunication and textile industries have made the Internet of Wearable Things (IoWT), the future of telemedicine. E-textile electrodes give us the ability for long-term monitoring applications; however, they are associated with electrode polarization impedance (Z(p)) contributing to the electrode-skin impedance (Z(es)). By studying the design of e-textile electrodes, we can reduce Z(p) and characterise it relative to changes in skin properties, such as skin temperature and perspiration. In this study, we examined the effects of selected textile substrates on changes in Z(p) of e-textile electrodes, and characterized Z(p) in a climatic chamber with temperature and relative humidity settings emulating skin temperature and perspiration. An air permeability test was also conducted to account for the physiological comfort of the e-textile electrodes. Our results demonstrate that a polyester non-woven felt substrate is ideal for use in e-textile electrodes. By understanding and quantifying the relationship between Z(p), skin temperature and perspiration, this insight can be incorporated into the calibration process of BIA systems for accurate long-term monitoring, resulting in an objective assessment of changes in tissue integrity. Spanish Government MINECOSpanish Government [TEC2016-79465-R] This work was supported by the Spanish Government MINECO under Project TEC2016-79465-R.

Harmonic oscillations of NACA 0012 airfoils in water are numerically simulated to assess the corresponding structural loads due to the generated forces. An appropriately devised procedure estimates the unsteady effect caused by the foil acceleration, i.e. the added mass effect. This is found to play a very important role as the resulting inertia forces are largely enhanced in the range of analysed parameters. The influence of the wing mass is investigated and it is found that light wings generate forces larger than those generated by heavy wings, as light wings accelerate more than heavy wings. The resulting bending stresses and unsteady deflections are calculated by modelling the wings as elastic cantilevers with uniform distributed loads. The maximum unsteady deflection is found to be about 1% of the wing span, that is, the fluid–structure interaction problem can be considered decoupled in the present analysis. It is also shown that heavy, rigid wings appear to be more suitable for the swimming mode corresponding to steady cruise, as the applied stresses result smaller than those obtained for light, flexible wings. The added mass effect could instead be exploited when required, by using lighter propulsors, which generate larger forces.

Unsteady effects caused by accelerating bodies in water play a very important role in biological propulsion. However, such propulsion mechanisms are challenging for simulation as both body geometry and locomotion patterns are quite complex and a natural first step is to model the motion of a standard man-made airfoil. The work presents simulations of harmonic oscillations of a NACA 0012 foil in water and the hydrodynamic forces generated were obtained by a Boundary Element Method (panel method) code. The focus is placed on one of the most important unsteady effects, the added mass effect, which has not been sufficiently addressed in the literature. The corresponding unsteady forces were obtained through appropriately devised two-dimensional added mass tensor. The computational results were compared to existing analytical ones and a maximum error of 10−6 was obtained for the added mass coefficients of the circle of unit diameter. The development of a dedicated numerical approach for the calculation of the added mass tensor is necessitated by the lack of analytical solution for a variety of wing shapes such as NACA foils. The simulations showed that for the range of investigated parameters the inertia thrust and lift generated by the flapping foil increase sharply when the added mass contribution is considered. For example, if the Strouhal number is set to 0.3 and the ratio between the wing and fluid densities to 0.3, the time average of the inertia thrust increases by 23 times and the maximum of the inertia lift is ca. 37 times larger when the added mass effect is considered. Generally, a densities' ratio of order 1 results in an increase of the time-average inertia thrust of order 10. It was confirmed that, as the densities' ratio becomes larger, the contribution of the added mass to the generated inertia forces decreased. As the Strouhal number increases, the added mass effect was found to be more dominant due to the imposed motion kinematics, i.e. the pitch amplitude. The obtained results show clearly that for the specific case of flapping flight in dense fluids the unsteady effects caused by the object acceleration are of prime importance for two reasons: (i) accurate estimate of the generated thrust and (ii) realistic assessment of the resulting structural loads.

Computational fluid mechanics (CFD) has made substantial progress on modelling a variety of important problems in industry. However, there is still lack of reliable methods to model the motion of the body in water. This is a central issue in understanding animal and human propulsion in water not only to advance science but to explore the possibility of utilising such propulsion modes for man made vehicles. The presented work identified the added mass effect as the prime contributor to propulsive force generation. The use of boundary element method (BEM) proved very successful as it allowed reducing this dynamic problem to a quasi-static one without sacrificing accuracy in the model. The comparison between the experimental data and the simulation result was in the range of 95% (average accuracy) suggesting that the added mass effect and dynamic lift and drag are the most significant physical phenomena in propulsive force generation despite the fact that there is undoubtedly and the presence of turbulent effects that were not considered.

Simulations of harmonically oscillating wings were performed using two-dimensional and three-dimensional boundary element method computer programs: the corresponding hydrodynamic forces were obtained by assuming potential flow. The maximum thickness of symmetric 4-digit NACA airfoils was varied in order to assess the effect of changing the foil shape on the generated thrust. It was found that the thrust coefficient per unit of wing mass decreases in magnitude when the thickness increases. The result indicates that, if the wing mass is fixed, its thickness has to be minimised in order to maximise the generated thrust. Another important finding is the dependence on the motion frequency, i.e. for a fixed foil thickness the thrust coefficient per unit of wing mass increases with the motion frequency. However, when the foil thickness becomes larger, the motion frequency effect on the generated thrust becomes less pertinent, i.e. the thrust range for a slender foil is larger than that of a thicker one over the same motion frequency range. The three-dimensional effect due to the wing spanwise shape was also investigated by changing the wing sweep angle and the influence on the generated thrust was insignificant within the range of investigated parameters. The outcome reinforces the idea that the function of swept wings for low-speed flyers, such as birds, is mainly structural as the sweep angle can be related to a desired aeroelastic response of the oscillating wing.

Trust generation by flapping wing is a complex fluid phenomenon involving unsteady effects. The work discusses a Boundary Element Method (BEM) based computer model for the analysis of hydrodynamic forces on flapping foil. The specific focus is on the wake model and its effects on the generated thrust. An unsteady formulation of the Kutta condition, assuming finite pressure difference at the trailing edge of the moving foil, was implemented in the numerical procedure to account for the shedding of trailing-edge vortical structures. It is shown that the numerical results depend strongly on the choice of the wake model, especially at large oscillation frequencies. However, the model of the thrust-producing jet (due to the trailing-edge pressure differences) predicts accurately the thrust trend as a function of the oscillation frequency. In other words, the numerical results show the need of experimental data in order to choose the appropriate wake model. An experimental validation of the numerical method is proposed on the basis of recent experimental results that clearly show the time lag between the foil vertical acceleration and generated thrust as predicted by the model. This proves the point that the unsteady BEM approach to these problems is physically sound.

The work represents a stage in the development of an integrated process for the analysis of biological objects – analytical image reconstruction from noisy data that allows fast dynamical analysis. The method also provides an interface to discrete methods such as finite element method (FEM). Two different methods are proposed – one is based on theta functions and the other uses analytical ellipsoids. Both methods possess built-in ability to remove noise from experimental measurements. The methods also have significant advantages if used in biological applications as it could process data directly from optical or general image devices such as cameras, microscopes and scans. Real-time online reconstruction and relevant computational analysis could be performed due to the rapid computational speed which in turn provides a good opportunity for the development of an integrated medical diagnostics technology. Both methods are demonstrated using appropriate examples.

A computer program based on a potential-flow panel method was developed to evaluate the hydrodynamic forces acting on a harmonically heaving and pitching two-dimensional rigid foil. A new formulation of the unsteady Kutta condition, postulating a finite pressure difference at the trailing edge of the oscillating foil, is proposed and implemented in the numerical procedure. A comparison with published experimental data [Anderson JM, Streitlien K, Barrett DS, Triantafyllou MS. Oscillating foils of high propulsive efficiency. J Fluid Mech 1998;360(1):41–72; Read DA, Hover FS, Triantafyllou MS. Forces on oscillating foils for propulsion and maneuvering. J Fluids Struct 2003;17(1):163–83; Schouveiler L, Hover FS, Triantafyllou MS. Performance of flapping foil propulsion. J Fluids Struct 2005;20(7):949–59] showed good agreement with the computational results. The analysis of the experimental results indicates clearly that robust computational procedures are necessary for reliable data processing in terms of calibration, noise removal, correction factors, etc. The proposed two-dimensional approach to the problem is currently being developed as a three-dimensional procedure that will address the unsteady flow effects such as inertia-related ones that are currently omitted.

A non-intrusive particle sizing method with a high spatial distribution is used to estimate cloud droplet spectra during flight test campaigns. The interferometric laser imaging for droplet sizing (ILIDS) method derives particle diameters of transparent spheres by evaluating the out-of-focus image patterns. This sizing approach requires a polarized monochromatic light source, a camera including an objective lens with a slit aperture, a synchronization unit and a processing tool for data evaluation. These components are adapted to a flight test environment to enable the microphysical investigation of different cloud genera. The present work addresses the design and specifications of ILIDS system, flight test preparation and selected results obtained in the lower and middle troposphere. The research platform was a Dornier Do228-101 commuter aircraft at the DLR Flight Operation Center in Braunschweig. It was equipped with the required instrumentation including a high-energy laser as the light source. A comprehensive data set of around 71¿800 ILIDS images was acquired over the course of five flights. The data evaluation of the characteristic ILIDS fringe patterns relies, among other things, on a relationship between the fringe spacing and the diameter of the particle. The simplest way to extract this information from a pattern is by fringe counting, which is not viable for such an extensive number of data. A brief contrasting comparison of evaluation methods based on frequency analysis by means of fast Fourier transform and on correlation methods such as minimum quadratic difference is used to encompass the limits and accuracy of the ILIDS method for such applications.